Method and apparatus using vibratory energy



Oct. 5, 1965 c. A. BOYD ETAL METHOD AND APPARATUS USING VIBRATORY ENERGY Filed Aug. 19, 1963 E m K y GR m w M F NYT 5 R 3:33 EQEQ wmm 0 36 a m k Q m A V W h w 0 av g I P W r. 1 :a x R w g B United States Patent 3,209,573 METHOD AND APPARATUS USING VIBRATORY ENERGY Charles A. Boyd and Herbert Kartluke, West Chester, Pa., assignors to Aeroprojects Incorporated, West Chester, Pa., a corporation of Pennsylvania Filed Aug. 19, 1963, Ser. No. 303,022

9 Claims. (Cl. 72-482) This invention relates to a method and apparatus using vibratory energy, and more particularly to a method and apparatus using vibratory energy in connection with drawing of materials.

It has been proposed heretofore, as in United States Patents Nos. 2,393,131; 2,568,303; and 2,638,207 to use vibratory energy in draw-forming operations, but these proposals have apparently never been commercialized. Various practical apparatus and methods have been disclosed in co-pending United States patent applications Serial No. 289,558 filed June 21, 1963, in the names of Charles A. Boyd et al., entitled, Method and Apparatus Utilizing Vibratory Energy; Serial No. 289,559 filed June 21, 1963, in the names of Charles A. Boyd et al., entitled Vibratory Energy Method and Apparatus; and Serial No. 289,694 filed June 21, 1963, in the names of Charles A. Boyd et al., entitled Method and Apparatus Employing Vibratory Energy. The disclosures of the said patent applications are incorporated herein by reference.

In the above-identified patent applications, the gross drawing tension depends upon operating parameters such as drawing velocity, reduction ratio, properties (such as tensil strength) of the material being drawn, and vibratory activation level. This gross drawing tension with vibratory activation is always lower than that which would be obtained under similar conditions but without vibratory activation. However, detailed examination of the variation of drawing tension at uniform drawing velocity with length of material drawn under conditions of vibratory activation shows that, in addition to the gross lowering of drawing tension pointed out above, there are periodic dips in the drawing tension at constant velocity corresponding to points of additional lowering in the drawing tension.

It has been found that these dips in drawing tension occur at certain resonant lengths of the drawn material, as will be explained hereinafter. The present invention provides a method and apparatus for insuring that the draw is made at a condition of drawing tension corresponding to the minimum value of tension obtained at the dips, thereby enabling greater reduction ratios than have been possible heretofore.

For the purposes of illustrating the invention there is shown in the drawings forms which are presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a graph generally illustrating drawing tension load conditions encountered heretofore in connection with the vibratory drawing of lengths of tubing at constant drawing velocity.

FIGURE 2 is an elevation of apparatus embodying the present invention, partly in section and partly in diagrammatic form.

FIGURE 2A is an enlarged sectional view of a fragment of the apparatus illustrated in FIGURE 2.

In the above-identified patent applications, no effort is made to obtain or utilize a resonant length of drawable material, such as tubing or wire. By this is meant a length definable in acoustical vibration terms, such as tubing whose physical length is equal to an acoustical length which (depending on the boundary conditions) is an odd or even integral multiple of one-quarter wavelength in the material and its geometry at the operating frequency of the apparatus and/or method. A resonant length of the article to be drawn is not a requirement in the said applications, and this is especially so because such a resonant length would be expected to change during the drawing operation. Thus, there would be changeeffecting factors such as the change in geometry necessarily imposed in connection with draw-forming, the damping effect of the clamping of the jaws of the pulling device on the article as it is drawn, the continual change in respective lengths of undrawn length and drawn length, the unwinding and winding of material on spools before and after drawing respectively, etc.

However, the vibratory apparatus used is perferably constructed so as to have an antinode or loop area of the vibration at the work-contacting end. No acoustical impedance match of the apparatus to the acoustical impedance of the drawable article is arranged for per se. However, it has been found that, in a given application wherein variable drawing tension forces are observed, a condition of resonance (with nodes and antinodes) is established in the drawn length. Thus, the aforesaid antinode or loop region of the vibration at the Workcontacting end of the apparatus will, under conditions of sufficient acoustic power, induce oscillatory particle displacements in the material being drawn, beginning at the contacting region between the apparatus and the article, as, for example, at the die. It is to be noted that a node may be defined as a region of minimum particle displacement, and an antinode or loop as a region of maximum particle displacement.

FIGURE 1 illustrates the general condition encountered heretofore with respect to drawing tension load at constant drawing velocity under vibartory-activation conditions, together with the defining of the dip intervals in acoustical vibration terms.

Thus, during most of the draw, the tension remains rather constant at a value T which value is lower than that encountered under non-vibratory-activation conditions, with the extent of lowering being dependent principally upon the factors of the amount of reduction, the tensile strength of the material, the drawing speed, and the amount of acoustic power applied. However, as can be seen, at certain discrete values of the length drawn, major dips occur in the drawing tension, as indicated by the value T, in FIGURE 1. For example, if T is 70 percent of the requisite drawing tension value for obtaining the material reduction without vibratory activation, then T, may be of the order of 50 percent of the unactivatedcondition value and therefore of interest as the optimum value of drawing tension if it can be constantly maintained during drawing.

It has been found, as aforesaid, that the discrete values of the material length drawn may be expressed in acoustical vibration terms. That is, the first interval occurs at a distance from the die of one-quarter wavelength ()\/4),

and subsequent dips occur at intervals of one-half wavelength (M2, where A is the vibratory wavelength in the drawn material computed from the frequency (f) of the activation system and the velocity (0) of compressional waves in the drawn material, in accordance with the well known equation:

Wavelength (A) tance of one-quarter wavelength AA). In this condition, there is an antinodal or loop region of vibration n the drawn article at the point where it contacts the die and/or plug. The clamping jaws constrain the other end of the drawn article to a nodal condition or position of no appreciable vibratory particle displacement. As the draw proceeds and the drawn article continues to lengthen, subsequent conditions of resonance will occur (with resulting tension load dips) at drawn lengths of km, /9, AA,

. .n/4 (where n=an odd integer).

It appears that, when the length of drawn article hecomes equal to the aforesaid lengths and thus exhlbits resonance, the input acoustical impedance from the activated die and/ or activated plug to the tubing or w re material goes through a minimum, and the particle displacement goes through a maximum.

Referring now to FIGURES 2 and 2A, there is shown a vibratory tube drawing apparatus designated generally as 10.

The apparatus 10 is in the nature of a draw bench and includes a die 12 having an orifice 14. A tapered plug 16 extends into or through the orifice 14 and defines with the die 12 a restricted pasageway through which the tube material 18 is drawn.

The rear end of the plug 16 is preferably removably connected (as by cooperating threads) to one end of an acoustical transmission or coupler element 20; where it is not necessary to provide a readily removable connection, the plug 16 and the element 20 may be metallurgically connected as by brazing. A washer (not shown) of a soft material such as aluminum may be disposed between the juxtaposed end faces of the plug 16 and element 20, which washer is compressed or deformed when the plug 16 is threaded to the element 20 to assure a good acoustic coupling if a screw connection is employed.

The transmission element 20 is preferably a resonant length of metal, such as steel (MAX-EL 3 /2 free machining steel, for example), aluminum-bronze, or Monel. By this is meant that element 20 will preferably have a length equal to a whole number multiple of one-half wave length, or an even number of one-quarter wavelength, in the material of which the rod is made at the frequency of operation. The combined length of plug 16 and element 20 preferably is dimensioned so that a loop or antinode area of the vibratory energy is juxtaposed to the die orifice 14.

The end of the acoustical element 20 remote from the plug 16 is joined, as by a threaded connection and lock nut 51, to one end of another acoustical coupler 22; the other end of coupler 22 is fixedly joined to a transducer 26, preferably by brazing or some other type of metallurgical joint. Elements 16, 20, 22, and 26 comprise a transducer-coupling system 24, which is dimensioned so as to operate at a given frequency, which is a resonant frequency. The purpose of the threaded connection and lock nut 51 between members 20 and 22 is to permit minor adjustments in the free length of coupler 20 to insure resonance at the frequency of operation. This is desirable because changes in the plug 16 to accommodate different diameters and wall thicknesses of tubing will affect the resonance of member 20. By shortening or lengthening element 20 via the threaded connection into element 22 and locking it in position with the lock nut 51, the effect of modestly differing masses and lengths of plug element 16 can be accommodated.

Acoustical coupler 22 is essentially a mechanical transformer and is of conventional single or multiple halfwavelength-long construction which is contoured for purposes of increasing amplitude of vibration. It may comprise a single member or, for purposes of manufacturing convenience, it may comprise a cylindrical portion metallurgically bonded or screw-connected in end-to-end contact with a tapered portion, the tapered portion by means 4 of its increasingly smaller cross section affording the increased amplitude. The tapered portion may be shaped so as to have a taper that is an exponential function of its length and satisfies the following equation:

where S is the reduced area at any section of the tapered portion, S is the area of the cylindrical portion, T is a constant describing the taper, and 1 is the length of the tapered coupler. This equation and the boundary conditions for resonance of a coupler such as coupler 22 are set forth at page 163 of Piezoelectric Crystals and Ultrasonics by Warren P. Mason, published in 1950 by D. Van Nostrand Company.

The transducer 26 may be of the magnetostrictive type and of conventional construction comprising a half-wavelength-long laminated core of nickel, nickel-iron alloy, or other magnetostrictive material, properly dimensioned to insure axial resonance with the frequency of alternating current applied thereto by coil 72 so as to cause it to increase or decrease in length according to its coefiicient of magnetostriction. The detailed construction of a suitable magnetostrictive transducer is well known to those skilled in the art and does not form a part of the present invention and, accordingly, no description of its construction will be made herein. It will be appreciated by those skilled in the art that in place of the magnetostrictive transducer 26 shown in the drawing, other known types of transducers may be substituted; for example, electrostrictive or piezoelectric transducers made of barium titanate, quartz crystals, lead titanate-lead zirconate, etc., may be utilized. Coil 72 is connected to a power supply (not shown) incorporating an oscillator and amplifier suitable for powering the transducer 26; such equipment is well known to the art. The transducer 26 is also provided with a polarizing coil 74, the desirability of magnetically polarizing the transducer 26 by means of polarizing coil 74, in order for the metal laminations in transducer 26 to efficiently convert the applied energy from excitation coil 72 into elastic vibratory energy, being readily understood by those skilled in the art. Low voltage direct current can be supplied to coil 74 by a battery as shown, or by a generator such as is used on an automobile, by rectifier, etc., such sources and their use in this conection are well known.

Preferably, and as shown more clearly in FIGURE 2, for support purposes and to minimize frequency shift of the vibratory apparatus and loss of vibratory energy to the associated supporting members, a force-insensitive mount 30 is attached to coupler 22. Such force-insensitive mount 30 may comprise a sleeve, one-half wavelength long at the operating frequency and made from steel or other low hysteresis material such as nickel, aluminumbr onze, beryllium-copper, or Monel. One end of the sleeve is metallurgically bonded to the coupler 22, preferably at an antinode or loop region on the cylindrical portion of the latter, and the other end of the sleeve is free from attachment. The sleeve is provided with a radially outwardly extending flange located one-quarter wavelength from the attached end, and a true node will develop at the flange. Reference is made to United States Patents Nos. 2,891,178; 2,891,179; and 2,891,180, each of which issued in the name of William C. Elmore and is entitled Support for Vibratory Devices. The flange is removably secured to a support 35 on a drawbench 36, as by a clamping ring 37 and suitable bolts. As shown to the left of FIGURE 1, support 35 is adjustably connected to the drawbench 36 via adjusting means such as a way slide 49 adjustable fore and aft in the direction of the action of the drawbench as indicated by arrow and arrows for longitudinal positioning of transducer-coupling system 24. Alternatively, a hydraulic cylinder means may be substituted for said Way slide 49.

A second transducer coupling system 38 includes die 12, acoustical coupler 40 (which includes a plurality of horns 44a, 44b and also 44c (and 44d not shown) and 'a plurality of transducers designated 50a, 50b, 50c, and 50d (the last not shown), respectively. System 38, like systern 24, is designed to operate at a given frequency, which is preferably a resonant frequency.

Each of transducers 50a, 50b, 50c, and 50d, is provided with an excitation coil 68 and a polarizing coil 70, and the description given hereinbefo-re as to transducer 26 is applicable to each of ma-gnetostrictiv-e transducers 50a, 50b, 50c, and 50d, including the fact that other types of transducers may be substituted in system 38.

As with excitation coil 72 of transducer 26, excitation coils 68 of transducers 50a, 50b, 50c and 50d, are connected to a power supply (not shown) incorporating an amplifier and oscillator suitable for powering the transducers 50a, 50b, 50c, and 50d.

The die 12 may have, for purposes of ease of attachment to coupler 40, an axially extending portion (not shown) to whose outer surface one end of coupler 40 is secured by means of cooperating threads. The other end of coupler 40 which is remote from the die, namely, each of the horn ends 44a, 44b, 44c and 444, is fixedly secured to a transducer; that is, horn end 44a is joined to transducer 50b, 44c is joined to 500, and 44d is joined to 50d, preferably by brazing or some other type of metallurgical joint.

Acoustical coupler 40 is essentially a mechanical transformer and is of contoured construction for purposes including the increasing of the amplitude of vibration. Reference is made to United States Patent Application Serial No. 114,932, filed June 5, 1961, in the names of James Byron Jones et al., entitled Tree Limb Vibratory Device for details concerning construction of a coupler such as coupler 40 and its associated plurality of transducers such as transducers 50.

The horn-type construction of system 38 is particularly suitable for application of relatively high levels of vibratory energy at a given frequency, and for avoiding undesirable modes of vibration in connection with both the powering and the operation of a relatively large single coupler, as well as for appropriate access and attachment to a member such as the die in order to vibrate it axially of the direction of passage of the tubing material.

For support purposes and to minimize frequency shift of the vibratory apparatus and loss of vibratory energy to the associated supporting members, the die 12 is sup ported by a force-insensitive mount 52, similar to forceinsensitive mount 30 hereinabove described. The mount 52 in the drawing comprises a conical tubular member (a form which is not necessarily preferred), one or more one-half wavelengths long, which is free of attachment at one end and joined at its other end to coupler 40. Mount 52 further includes a flange (like the flange of mount 30) for connecting the mount 52 to a support 60, as by a clamping ring 61 and suitable bolts. Support 60 is rigidly secured to the drawbench 36.

It will be appreciated that, instead of being formed and positioned as shown, mount 52 may comprise a plurality of more or less rodlike members, all having flanges and some being attached to each of the straight portions of horns 44a, 44b, 44c, and 44d. This may be desirable, as, for example, in associating mount 52 with coupler 40 in the section not representing an increase in amplitude of vibration, thereby minimizing the subjection of mount 52 to the increased stresses associated with the maximum amplitude implicit to the contoured portion. If this latter configuration is used, the position of the support members relative to the drawbench will also be adjusted accordingly.

A lubricant may be applied to the inner and/or outer surfaces of the tube 18 by means well known in the art.

In a typical example, the power supplies a'b-ove mentioned are capable of producing electrical signals in the range of between about 60 cycles per second and about 300,000 cycles per second. This frequency range is suitable for purposes of the present invention, including as it does frequencies in both the audible range (such as up to about 15,000 cycles per second) and the ultrasonic range (generally about 15,000 to 300,000 cycles per second). A preferred frequency would be in the range of from about 3,000 to about 50,000 cycles per second with the optimum being between about 14,000 to about 35,000 cycles per second. Normally, a frequency is chosen which will provide a suitable size of apparatius for a given application or set of applications.

Thus, transducer-coupling systems 24 and 38 may be each constructed to operate at 15,000 cycles per second tor example.

As is well known to the art, the electrical frequency of the alternating current power supply (such as 60 cycles per second) is changed to match the mechanical or elastic vibratory frequency of the transducers (15,000 cycles per second in this example, as aforesaid).

It is to be noted that the source of high frequency alternating current may be a motor alternator having suitable frequency control, and that such a motor source is particularly appropriate for drawing applications requiring large amounts of power.

In operation a tube 18 is telescoped over the plug 16 and element 20. The tube 18, in accordance with standard practice, is provided with a reduced outside diameter end portion, which may be accomplished in a variety of ways including swaging. Such reduced portion is fed in the direction of arrow 90 through the die orifice 14. The jaws 64a and 64b of a pulling device 62 are clamped to the reduced end portion of the tube 18. Pulling device 62 is movably mounted on drawbench 36 for pulling the tube 18 through the passageway defined by die 12 and plug 16. The pulling device 62 is first actuated in the direction of arrow 90 to seat the plug 16. That is, the tube 18 is pulled in the direction of arrow 90' until the tube 18 is locked between the die orifice 14 and the outer peripheral surface of the plug 16.

The tube 18 can be translated by the pulling means for a short distance, so that the plug will seat properly and drawing can be readily accomplished; however, the invention is not limited to any particular sequence of steps in seating the plug, although certain sequences are far more favorable. As is readily evident, various lengths of tubing may be accommodated in accordance with the present invention.

After the plug 16 is properly seated and positioned, as, for example, by means of the way slide system and supporting transducer-coupling system 24, and vibratory energy is applied to the plug and/or the die, the pulling device 62 will move the jaws 64a and 64b in the direction of arrow 90. A wide variety of devices may, of course, be utilized to pull the jaws 64a and 64b, such as a hydraulic cylinder, a cable Windup device, a rack and pinion trolley device, etc. It will be appreciated that the jaws 64a and 64b will be provided with means for selectively opening and osing the same, so that the redued end portion of the tube 18 may be inserted and gripped therebetween.

In accordance with the present invention, the drawing apparatus 10 is also provided with a second die designated having a die orifice 81. Die 80 is not vibratorily activated and is preferably, for eflicient operation, acoustically non-complaint and may therefore be referred to as an inert die. Die 80 is positioned to the downstream side of the apparatus at such a distance from die 12 that the drawn tubing between the die 12 and the die 80 has a physical length representing an asoustical length in the drawn tubing of It)\/4, where n is an odd integer, such as l, 3, 5,

Die 80 has a die orifice diameter such as to cause a slight sink in the drawn tubing, which sink is great enough to cause the drawn tubing to be held so as to prevent or minimize vibratory particle motion therein at the die 80 location along the tubing. With this geometry, a permanent condition of resonance is maintained in the section of tubing between the active die 12 and the inert die 80, and the acoustic impedance from the activated die 12 and/or activated plug 16 into the tubing is always at a minimum; this maintains the drawing tension at a minimum for the reasons described above.

The position of the die 80 may be adjustable close to and away from die 12 (as by adjusting means 84), to allow for start-up of the method and apparatus sufficiently to allow determination of n \/4 positions in the drawn wire, or drawn tubing, or other drawn geometry.

Since, as is well known to the acoustics art, the velocity of compressional waves in a medium varies according to the medium, and in view of the above-indicated well known equation showing the relation among frequency, velocity, and wavelength, the arrangement and utilization described herein of the inert die 80 (whether or not the die 12 is vibratorily activated) will vary according to the material being drawn and the frequency of vibration involved. Various examples are given in the following table:

For example, in connection with the drawing of copper tubing having an CD. of 0.250-inch and an I.D. of 0.20- inch:

With vibratory-activation of the plug in accordance with FIGURE 2, at a frequency of 15 kc. and a power input to the transducer of 400 watts, using a drawing velocity of five feet per minute, the drawing tension was generally 450 pounds, with tension load at the dips being 400 pounds. In accordance with the present invention, the lower drawing tension of 400 pounds can be maintained, using an inert die spaced about 2.3 inches from the activated plug end, i.e., at the M4 location for copper at 15 kc.

Likewise, with vibratory activation of the die 12 in accordance with FIGURE 2, at a frequency of 15 kc. and a power input to the transducer of 2,000 watts, using a drawing velocity of about two feet per minute, the drawing tension was generally 220 pounds, with tension load at the dips being 165 pounds. The lower 165-pound tension load could be maintained using an inert die spaced as indicated above, namely, about 2.3 inches from the vibratorily-activated die 12.

With vibratory activation of both the plug 16 and the die 12 in accordance with FIGURE 2, at a frequency of 15 kc. and power input to the die transducer of 1,000 watts and to the plug transducer of 250 watts, using a drawing velocity of five feet per minute, the drawing tension was generally 230 pounds, with tension load at the dips being 200 pounds. The lower 200-pound tension load could be maintained using an inert die spaced the aforesaid 1/4 or about 2.3 inches along the copper material from the activated area where the vibratory energy is introduced to the copper tubing by the die and plug combination.

If the tubing material had been aluminum or steel, or if the frequency of operation had been 20 kc. or 30 kc., or some other frequency, or if some other drawable material had been used (drawable material referring to materials and/or geometries drawable under vibratory activation conditions, inasmuch as some materials, configurations, and reduction ratios are drawable under vibratory activation conditions which are not otherwise drawable) at a given frequency of activation, the quarterwavelength dimensioning would vary accordingly. Such dimensions are readily available to or ascertainable by one skilled in the art. Also, it is not necessary to know the activating frequency and calculate the appropriate spacing dimension, since a minor amount of testing by an operator will sufilce to locate the regions of dips in tension load, and the inert die can then be adjusted for firm positioning at the dip location obtained by such testing, after which the drawing operation can proceed into production of the length of drawn material desired. Such an adjustable setting is to be preferred, for greater accuracy of spacing dimensions, inasmuch as pre-calculated dimensions may not permit of allowance for minor differences attributable to factors such as differenct materials (such as different alloys), non-isolated mounting of the apparatus, temperature effects, faulty joints, etc.

Either the system 24 or the system 38 or both may be used in connection with the present invention. That is, tube drawing, for example, can be used with a die in conjunction with a vibratorily-activated plug system alone, or a vibratorily-activated die system alone, or with a combination of the two.

It will also be appreciated that the inert die described herein may also be used on the upstream side of the die 12, rather than on the downstream side as described and shown herein, so long as access to the outer surface of the tubing is available in a manner suitable for purposes of the present invent-ion, and so long as said inert upstream die is located within reasonable distance of the die 12. Such an upstream or downstream arrangement, if the position of the inert die is adjustable for purposes of the present invention, can utilize sinking dies already used in some commercial drawing operations in conjunction with drawing dies.

The power input of the transducer or transducers may be varied according to the operating conditions utilized, including the material being drawn, and also according to the transducer-coupling system or systems employed.

As is well known to those skilled in the art, power output (to the work) of acoustical vibration devices is not readily ascertainable directly, and indirect determination thereof often involves the use of liquids and other aspects not suitable for ready adjustment to differing industrial applications. Moreover, permissible power input is variable according to the type of transducer utilized and the acoustical coupler geometries and materials used, as well as such factors as the efiiciencies of joints between the various members of the transducer-coupling system. For example, a magnetostrictive transducer is far more rugged and trouble-free than a ceramic transducer, but it has a lesser efiiciency in converting electrical power into mechanical vibration, and steel is a more readily machinable and joinable coupler material than Monel or beryllium-copper but it has a lesser acoustical transmission efficiency. The implications are obvious for differing amounts of acoustic power (expressed in electrical watts output from the power supply or input to the transducer) used with various equipment, even without taking a given drawing reduction into consideration.

For those desiring to insure continued transmission efficiency of a given system (in order to obtain warning of malfunction, for example), or for those desiring to compare the relative transmission efficiencies of a plurality of systems, means may be used such as are described in co-pending patent application Serial No. 66,642 filed November 1, 19-60 for Method and Apparatus for Measurement of Acoustic Power Transmission and Impedance by Dennison Bancroft et al.

For purposes of insuring a sufficient level of acoustical energy for purposes of the present invention, it is to be noted that provision has been made, in addition to a sufficient level of electrical power input to the transducer, for acoustical amplitude transformation. Also, this acoustical amplitude transformation should preferably involve, when a magnetostn'ctive transducer is used, a total transform-er ratio (from the driving face of the transducer to the point of energy utilization) in the range of about 3.0 to 7.5; when an electrostrictive transducer (such as one of lead zirconate titanate) is used, such transformer ratio should preferably be in the range of about 1.5 to 5. This ratio depends in part upon the material or materials of which the coupling system member or members is made.

The transformer ratio is of particular importance for purposes of most efiicient (and most economical) utilization of the vibratory energy for drawing.

As indicated by the above-identified patent applications, the natural limits imposed upon drawing operations by the physical properties of a given material (such as tensile or yield strength and hardness) may be circumvented to some extent by the inventions therein, which enable greater reductions than have been possible heretofore and/or the use of lesser drawing tension and/or greater drawing speed, while at the same time there is a lesser temperature increase in the material than occurs in conventional drawing of a given material reduction. To this, as aforesaid, the present invention contributes the ability to maintain drawing tension at a substantially constant lower level, thereby circumventing material properties still farther.

It is to be noted that the apparatus described herein is arranged to be isolation-mounted, so as to avoid undesirable transfer of acoustical energy from the transducer-coupling system to the drawbench per se and/or from the drawbench (because of inherent resonances therein) to the work and/ or transducer-coupling system.

A tapered plug (such as one of tungsten carbide is shown in FIGURE 2, although other geometries and materials may be suitable for the purpose, and a freefloating plug may also be used instead of a back-supported plug such as is shown. A beryllium-copper acoustical element inch in diameter at kc.;

%=4.9 inches in length) attached to the back-supported plug is more efficacious than a steel element for reasons of more efiicient acoustical power delivery also; although having (in conjunction with the plug) the same acoustical wavelength (57 onehalf wavelengths in a typical instance), it will be physically somewhat shorter than the steel element.

As aforesaid, if a plug-activation system is used, either alone or in combination with die-activation, this invention is not limited to any particular sequence of steps in seating the plug, and the order of seating in the operation is not critical to the present invention. For example, and as may be particularly desirable in applications contemplating relatively higher area reductions per pass for a given material, the plug and/or die systems may first be energized, the reduced cross section end of the tubing may be threaded through the die orifice (with or without assistance of the pulling device, which device may aid in a desirable amount of sinking of the reduced cross section end of the tubing), and the plug may then be advanced into the tubing and seated as desired. Advance activation of the plug and/or die systems before seating of the plug or tubing may serve to simplify production operations. It may also minimize likelihood of undesirable tubing metal pickup by the unenergized plug and/or die during seating, such as may be encountered with certain materials, or with relatively high area reductions for a given material.

For efficient operation, the pulling device (including the jaws 64a and 64b) should be acoustically non-compliant. That is, the pulling device should not resonate in any mode at the frequency of operation, or at any frequency related thereto, but should be essentially acoustically non-responsive, a condition attainable by various known means including appropriate adjustment of mass.

Although the invention is shown and described herein in connection with the drawing of tubes, it is to be understood that the invention is applicable generally to the drawing of elongated articles having wall structure formed at least partly about a longitudinal axis thereof, including the drawing of wire.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the inven tion.

We claim:

1. Article forming apparatus comprising a first die having an orifice, means for oscillating said first die, means for moving an article through said orifice, said means for oscillating said first die oscillating at a given frequency, and a second die spaced from said first die through which the article will be moved, said second die being spaced an odd integral multiple of one-quarter wavelengths of sound in the material and geometry of the article at the given oscillating frequency from said first die.

2. The article forming apparatus of claim 1 including a plug partially extending into said orifice and cooperating with said orifice to define an annular passageway through which an article will move, a discrete vibratory means coupled to said plug for vibrating said plug independently of the vibration of said first die.

3. The article forming apparatus of claim 1 wherein said means for moving an article includes article pulling apparatus adapted to pull one end of an article, said second die being spaced between said article pulling apparatus and said first die.

4. The apparatus of claim 1 wherein said second die is acoustically non-compliant, and means adjustably spacing said second die one-quarter wavelength from said first die.

5. The apparatus of claim 4 wherein said second die having a die orifice opening sufficient to cause a slight sink in the drawn article so as to prevent vibratory particle motion at said second die.

6. A method of drawing articles comprising the steps of providing a die, feeding a reduced diameter portion of an article through said die, coupling vibratory energy to said die, pulling said reduced diameter portion in an axial direction away from said die to reduce the crosssectional area of said article as it passes through the die, providing an inert die spaced one-quarter wavelength of said article at the frequency of the vibratory energy applied to said first mentioned die from said first mentioned die, and passing said article through said inert die.

7. A method of drawing tubes comprising the steps of providing a plug at one end of a transmission element so that a vibratory l-oop occurs in the plug, telescoping a tube around the element and plug, supporting the other end of the element, feeding a reduced diameter portion of said tube through a first die, feeding said plug against a portion of said tube juxtaposed to an orifice of said die, coupling vibratory energy to said plug, pulling said reduced diameter portion in an axial direction away from said first die to reduce the cross-sectional area of said tube as it passes through said first die, providing a second die spaced one-quarter wavelength of sound in the material and geometry of said tube at the frequency of the vibratory energy applied to said plug from said first die, pulling said tube through said second die to further reduce the cross-sectional area of said tube.

8. The method of claim 7 wherein said step of providing a second die includes providing an inert die orifice whose diameter causes a slight sink in the drawn tubing so as to prevent or minimize vibratory particle motion at the inert die location along the tubing.

9. Tube drawing apparatus comprising a first die having an orifice, vibratory means coupled to said die for oscillating said die at a given frequency in an axial direction with respect to said orifice, a second die spaced from said first die by a distance corresponding to an odd integral multiple of one-quarter wavelength of sound in the tube material and geometry of the tube to-be-drawn at the given oscillating frequency of said first die, a discrete means for adjustably supporting said second die with respect to said first die, a plug partially extending into said orifice and cooperating therewith to define an annular passageway through which a tube may be drawn, a coupler element coupled to said plug and around which the tube to be drawn may be disposed, and a discrete References Cited by the Examiner UNITED STATES PATENTS 2,568,303 9/51 Rosenthal 20525 3,002,614 10/61 Jones 2072 FOREIGN PATENTS 955,943 1/57 Germany.

CHARLES W. LANHAM, Primary Examiner.

MICHAEL V. BRINDISI, Examiner. 

1. ARTICLE FORMING APPARATUS COMPRISING A FIRST DIE HAVING AN ORIFICE, MEANS FOR OSCILLATING SAID FIRST DIE, MEANS FOR MOVING AN ARTICLE THROUGH SAID ORIFICE, SAID MEANS FOR OSCILLATING SAID FIRST DIE OSCILLATING AT A GIVEN FREQUENCY, AND A SECOND DIE SPACED FROM SAID FIRST DIE THROUGH WHICH THE ARTICLE WILL BE MOVED, SAID SECOND DIE BEING SPACED AN ODD INTEDGRAL MULTIPLE OF ONE-QUARTER WAVELENGTHS OF SOUND IN THE MATERIAL AND GEOMETRY OF THE ARTICLE AT THE GIVEN OSCILLATING FREQUENCY FROM SAID FIRST DIE. 